In 2012, the US Advisory Committee on Immunization Practices (ACIP) began recommending a Tdap (tetanus, diphtheria, and pertussis) vaccine be administered from 27 to 36 weeks' gestation in each pregnancy.

The rationale was that the inactivated vaccine would pass on maternal antibodies for pertussis, or whooping cough, a serious illness in infants. Maternal antibodies would be protective until the baby received its first of Tdap, at 2 months of age.

"Now we have data that shows this is actually working," said Paul Cieslak, MD, medical director, Communicable Diseases and Immunizations at Public Health Division at Oregon Health Authority, in an interview.

Cieslak is referring to a study published yesterday in Clinical Infectious Diseases that shows that 78% of babies 2 months old and younger were protected from pertussis if their mothers received the Tdap vaccine in the third trimester of pregnancy.

90% protection against severe cases…

While Cieslak, an author of the study, said that UK data have shown 90% protection rates in newborns, but this is the first multistate, multicenter US study to demonstrate that the Tdap recommendation is useful and effective. And protection equaled UK rates when looking at severe pertussis cases.

"Ideally, mom gets the shot before 36 weeks, and we have at least 2 weeks before the delivery for the mother's body to mount antibodies that are actively passed through the placenta," said Cieslak.

The data were collected from six states between 2011 and 2014, and a case-control evaluation among pertussis cases in infants under 2 months old were compared with healthy infants of the same age. The study included 240 cases and 535 as controls.

When Tdap was administered to the mother in the third trimester, vaccine effectiveness against pertussis in the newborns was 77.7%, and it reached 90.5% against hospitalized pertussis cases.

According to the US Centers for Disease Control and Prevention (CDC), 5 to 15 babies die each year from pertussis, and 65% of babies younger than 2 months who contract the disease and suffer its severe, violent cough will require hospitalization.

…but low vaccine uptake

While the study was a strong affirmation of ACIP's standing recommendation, the CDC said only 49% of pregnant women who delivered in 2015 and 2016 received the vaccine.

"We have decades of evidence that inactivated vaccines are very effective and safe in pregnancy," said Cieslak. "And each pregnancy a woman has needs the Tdap to offer baby protection against whooping cough."

"We haven't seen a single safety signal rising in recent years," he added.